Apparatus for heat treating thermoplastic yarns



Jan. 8, 1963 E. P. R. SCRAGG 3,07

APPARATUS FOR HEAT TREATING THERMOPLASTIC YARNS Filed April 16, 1959 W Qw W M 6 W MM/ 4 G MM ,4 7 6 F W i 1 M I .fvb B 5 z 5 6 U/ M H n UnitedStates Patent 3,071,838 APPARATUS FOR HEAT TREATING THERMOPLASTIC YARNSErnest Philip Rushton Scragg, Alderley Edge, England, assignor to ErnestScragg & Sons Limited, Macclesfield, England Filed Apr. 13, 1959, Ser.No. 805,913

Claims priority, application Great Britain Aug. 19, 1958 3 Claims. (Cl.28-62) Our invention relates to a method and to apparatus for heattreating thermoplastic yarns in a continuous manheater, this temperaturebeing such as to affect the molecular structure of the yarn in anyrequired manner, i.e., it may relieve internal stress in the yarn, itmay cause the yarn to shrink or allow it to extend its length, or it mayset twist in the yarn.

Hitherto, it has mainly been the practice, more particularly when theyarn is heated by radiation from a heated surface without contact withit, to cause the heated zone to have a restricted cross-section. Thiswas thought to be necessary in order both to increase the rate of heattransfer to the yarn and also to reduce heat loss by cooling of the yarnand the heated surface by air currents flowing up the heated tube byconvection. Whilst both these eifects are of course obtained, we findthat an undesirable result also occurs. This eifect is the production offumes in the heated zone from the yarn, these fumes presumably beingmonomers or breakdown products derived from the surface of the polymerof which the yarn is composed. The fumes tend to condense and collectinto a hard black adhesive deposit at the top of the heated zone. Thisdeposit occurs particularly in the case where the heated zone is a tubehaving substantially uniform circular cross section, of a diameter notgreatly exceeding that of the yarns being treated.

We have found that the adoption of a substantially unrestricted form ofheat zone, whilst not necessarily being associated with a greatlyincreased heat loss, does very much reduce the deposition of condensedmonomer at the top of the heating zone, and this is thought to be due toan increased rate of convectional air flow upwards over the face of theheated zone.

It is, therefore, an object of the present invention to provide aheating method and heating device for travelling yarns which avoidsdeposition of fumes in the heated zone.

Another object is the provision of such a method and device whichremoves fumes from the heated zone vwalls of the heated zone to aminimum.

A further object is the provision of a heating method and device fortravelling yarns which aifords maximum heat transfer to the yarn as itpasses through a heated zone.

An additional object is the provision of such a heating method anddevice in which the temperature of the heated zone increases graduallyin the direction of travel of the yarn, so that the yarn is heatedslowly to the desired temperature.

It is furthermore an object of this invention to pro vide such a heatingdevice which is simple in its structure and operation.

With these and other objects in view, the method of the invention forheat treating a travelling yarn of the type described contemplatespassing the yarn in an upward direction through a heating zone which hastwo contiguous portions longitudinally extending in the direction oftravel of the yarn. Each of these portions has an end open to theatmosphere andtapers from this end in- -Wardly in the heating zonetoward a common plane of minimum cross section. The yarn is heated inthe heating zone by conduction. Simultaneously, the air in the heatingzone is heated so that a thermally induced current of air is provided inthe zone for removing fumes derived from the heated yarn.

To carry out the above-described method, it is proposed to employ aheating device having a body of heat insulating material formed with anelongated conduit therethrough for passage of the yarn. Elongatedheating plate means are provided in the body. A convexly curvedlongitudinal face portion on the heating plate means forms a convexlongitudinal wall of the conduit so as to define therein two contiguouslongitudinal portions each tapering from the outer surface of the bodyof heat insulating material toward a common plane of minimum crosssection in the conduit.

In one specific embodiment of the invention, the heated zone comprises aheated plate which is slightly curved into a convex form, the platehaving one or more longitudinal grooves formed in its surface, the yarnbeing arranged to run in each groove. The heated plate is located at thebottom of a U-shaped channel the sides of which are composed ofinsulating material, the outer or open end of the U being eitheruncovered or provided with a flat or curved cover, the shape of thecover being such as to produce or permit an appreciable flow of air overthe surface-of the heated plate. The cross-sectional 'area of theU-shaped channel at its minimum is preferably several thousand times aslarge as that of the normal yarn of say denier being treated by theapparatus concerned.

In an alternative specific embodiment of the invention, a curved heatedplate is once more provided, the surface of the plate being continued asby insulating material so as to form a figure of revolution generatedfrom a linev in front of the plate and substantially parallel to itsmajor axis, the cross-section of the said figure being a minimum at apoint rather above the centre of the curved plate, the curvatures of theplate and the air channel formed by the figure of revolution being sodevised as to produce a maximum rate of convectional air flow. I Ifnecessary, the upper end of the said channel may be flared so that anymonomer fumes produced tend to pass straight face on which condensationmay take place.

In the case where a U-shaped figure is adopted for the yarn channel,with an opening to the atmosphere at the open end of the U, the depth ofthe U is preferably not less than 250 times the diameter of the yarntreated, and its width is preferably not less than 100 times the saiddiameter.

One advantage of the form of heater described is that a temperaturegradient is secured along the surface of the heater. This is desirablenot only to ensure gradual heating of the yarn, but also to establishcountercurrent conditions of heating, i.e., the hotter the yarn becomes,the hotter the surface with which it is in contact. With some knownforms of heater having channels of restricted cross-sectional area forthe yarn, it has been the practice to establish a uniform temperaturethroughout the whole of each channel, as for example by grading theheater winding. We have not found such uniformity to be essential oreven desirable, so long as the first temperature achieved by the yarn isitself constant and of a predetermined value. In fact, if oil heating ofthe plate is employed we prefer to cause the oil and yarn to travel inopposite directions from one another.

The novel features which are considered as characteristic for theinvention are set forth in particular in the appended claims. Theinvention itself, however, both as to its construction and its method ofoperation, together with additional objects and advantages thereof, willbe best understood from the following description of specificembodiments when read in connection with the accompanying drawings, in.which:

FIG. 1 is an elevational sectional view of a preferred embodiment of theinvention; 7

FIG. 2 shows the device of FIG. 1 in transverse section line on lineII-II of FIG. 1;

FIG. 3 is an elevational sectional view of another preferred embodimentof the heating device of the invention;

FIG. 4 illustrates the device of FIG. 3 in transverse section on lineIVIV of FIG. 3;

FIG. 5 shows a third embodiment of the invention in elevational section;and

FIG. -6 is a transverse sectional view of the device of FIG. 5 taken online VI--VI of FIG. 5.

Referring now to the drawings, and more particularly to FIGS. 1' and 2,there is shown an elongated thin heater. plate 1 of heat-conductivematerial longitudinally curved into a convex form. The convex surface ofthe plate. 1 is curved transversely in such a manner as to form twolongitudinal channels 2 in the heater plate 1. Theheater plate 1 isarranged in a slot 3 of a block of heat-insulating material such asmolded asbestos material or a metal shell filled with glass wool. Theslot 3 has one. convexly curved wall formed by the surface of the heaterplate 1 and an open side opposite the convex wall. The. open. side ofthe slot 3 is closed by a removable cover 5.

An electric heating element fi is embedded in the surface of the convexwall of block 4 in the slot 3. in contact with the heater plate 1. Theheating element 6 is of conventionalconstruction so as to provide asubstantially uniform heat density along the length thereof and receiveselectric energy through leads 9 passing through the block 4.

Two strands of yarn 7 are guided by means of guides 8 in such a mannerthat they make tangential contact with the curved heater plate .1 atpoints slightly inward 'ofthe orifices of the channel defined in theslot 3 by the facing surfaces of the heater plate 1 and of the cover 5.As best seen from FIG. 1, the channel is shaped in "such a manner thatit is widest at its orifices and graduallyt'apers towards a middleportion.

The device described above operates as follows:

The strands of yarn 7 are passed through the heating device of theinvention from the bottom to the top by suitable means such as paireddriven pull rolls. Thermal energy is supplied to he heater plate 1 bythe heating ele- As is well known from the design of Venturi tubes andcooling towers for power stations, the shape of the channel thecross-section of which decreases toward the enter of the heater plate 1and then again increases causes at first an increase in speed of the airentering the slot 3 from the lower end. The cross-section of the aircolumn decreases as its velocity increases. During this period, heat isgained by the air. On passing the area of smallest cross-section in thechannel, the air is allowed to expand, thus providing a negativepressure at the narrowest part of the passage.

This design of the channel produces an appreciable current of airupwards through the heater, the said current causing any fumes which maybe derived from the heated yarn to be rapidly carried away from thevarious parts of the heater, which are consequently kept clean. We findthat if some such means as the foregoing is not adopted, fumes from theyarn tend to condense as a black highly adhesive deposit on parts of theyarn passage near the top, the said passage becoming obstructed after aperiod of time.

As regards the dimensions of the various parts concerned, thecross-sectional area of the channel at its minimum is preferably severalthousand times the cross-sectional area of the yarn being treated, asotherwise an in suflicient draft is created. In spite however of thisdraft, we find that by careful insulation of the heater the total powerconsumption can be kept within such bounds that a textile machine fittedwith say, heaters can be operated in a relatively small room withoutundue rise of temperature or serious decrease in the relative humiditytial thicknes and provided with a single channel 2 cut into I the convexsurface of the heater plate 1; The plate is cored so as to provide apassage 10 for heating oil which is admitted to the passage 10 at theupper orifice 11 thereof and is returned from a lower orifice 12 to aheating and circulating device which provides thermal energy to theheating oil and causes it to pass through the passage 10 in a downwarddirection. Such heating and circulating devices are well known andmayconsist of a tube of heat-conductive material exposed to a flame oranother source of heat. Circulation of the oil may be caused by thermalsyphoning, or a suitable circulating pump may be included in the oilcircuit. a

The heater plate 1 of FIGS. 3 and 4 is embedded in a block 4 ofinsulating material and has a convex surface: in a slot 3 which has anopen side opposite the heater plate 1. Guides 8 are provided to guide asingle strand of yarn 7 towards and away from the heater plate 1 in themanner described above in connection with the em-- bodiment of theinvention shown in FIGS. 1 and 2. I

A cover 5 may be inserted in the slot 3 of the block 4'. The cover 5'consists of insulating material and has a convex face portion 13 whichwhen inserted in the slot 3 forms a channel with the convex surface ofthe heater plate 1' and with the parallel faces of the block 4 in theslot 3. The channel has the sectional shape of a Venturi nozzle.

The device illustrated in FIGS. 3 and 4, when operated with the cover 5'inserted in the slot. 3, operates in the plate 1 of FIGS; 3 and 4 mayhave a substantially a greater radius of curvature than the heater plate1 of FIGS.- 1 and 2. Conversely, for equal radius of curvature of theheater plate 1', the Venturi effect of the device of FIGS. 3 and 4 isenhanced.

Whereas the electric heating element 6 of the firstdescribed embodimentof the invention has a uniform heating rate over the entire lengththereof, the oil heating system shown in FIGS. 3 and 4 results in a rateof heat supply which gradually decreases from the top of the heat plate1' towards the bottom as the temperature of the oil drops in the passage10 when the oil travels from the upper orifice 11 to the lower orifice12. In either case, the temperature of the heater plate is highest atthe topmost portion thereof because of the upward flow of air from theatmosphere which has a greater cooling effect as it enters the heatingdevice at the bot tom than in the higher portions of the heated channel.The yarn 7 thus is in contact first with a portion of a heater platewhich is at a temperature lower than the maximum temperature to which itis desired to heat the yarn, and this maximum temperature is onlygradually reached. Such relatively slow heating of the yarn during itspassage through the heating device has been found desirable in manyinstances.

The devices illustrated in FIGS. 1-4 may also be operated without thecovers 5, 5'. While the devices of FIGS. 1-4 are not as effectivewithout the covers 5 and 5' in creating an air draft over the surface ofthe heater plate, omission of the cover reduces the first cost of theheating device somewhat, and its operation is nearly as satisfactory asregards removal of yarn fumes from the apparatus. Threading is, ofcourse, greatly simplified. The slot should be large as compared withthe yarn, its depth being preferably not less than 250 times thediameter of the yarn treated, and its width preferably not less than 100times the said diameter.

A third embodiment of the invention is illustrated in elevational andtransverse section respectively in FIGS. 5 and 6. In this embodiment, aheater plate 1" having a convexly curved front surface is fitted into arear heat insulating member 14. The heating device furthermore includesa front insulating member 15 having a channel 16 formed therein. Theedges of the channel are in contact with the heater plate 1". The shapeof the interior surface of the channel 16 is that of a figure ofrevolution generated from a line in front of the heater plate 1" andsubstantially parallel to its general direction. The crosssection of thefigure is generally circular and is at a minimum just above the centerof the heater. The inner surface of the channel 16 is smoothly curved.An electric heating element substantially identical with thatillustrated in FIGS. 1 and 2 is embedded in the rear heatinsulatingmember 14 in contact with the heater plate 1 (not shown).

The embodiment of the invention illustrated in FIGS. 5 and 6 operates inthe same manner as those of FIGS. 1-4 when equipped with theirrespective covers 5 and 5. The specific form of the device illustratedin FIGS. 5 and 6 encourages the maximum flow of air over the surface ofthe heater for a given cross-sectional area of channel.

All of the foregoing embodiments are devised in order not only to giveminimum radiation heat loss from the metal heater plate, but alsomaximum heat transfer by conduction from the plate to the yarntravelling over it, and maximum induced air flow through the channel soas to cause removal of any fumes formed from the yarn during its passageover the plate.

In view of the fact that fumes are emitted constantly from the top ofthe assembly, it is advisable to construct the rest of the machine insuch a fashion that no cool metal surfaces are located immediately abovethe said channel. On the other hand, it may be found advisable to hang areadily removable or cleanable screen above the said channel but atsuch. a distance from it as not appreciably to affect the flow of airthrough the said channel. The heat lost to the air flowing through thechannel is of course appreciable but we find that the freedom fromobstruction and continuity of service enjoyed by the particularapparatus described makes the loss worthwhile.

It will be understood that each of the elements described above, or twoor more together, may also find a useful application in other types ofheating devices differing from the types described above.

Without further analysis, the foregoing will so fully reveal the gist ofthe present invention that others can by applying current knowledgereadily adapt it for various applications without omitting featuresthat, from the standpoint of prior art, fairly constitute essentialcharacteristics of the generic or specific aspects of this inventionand, therefore, such adaptations should and are intended to becomprehended Within the meaning and range of equivalence of thefollowing claims.

What is claimed as new and desired to be secured by Letters Patent is:

1. In a heating apparatus for heating travelling yarns, in combination,an elongated heating member having a longitudinal, convexly. curvedheating surface adapted to be contacted by yarn travellinglongitudinally of said surface; and elongated heat insulating means atleast as long as said heating member formed with a longitudinal cutoutin which the entire heating member is located extending longitudinallyof said insulating means, the latter having at said cutout thereof aconfiguration which forms with said heating surface an elognated passagewhich from one to the other of the ends of said heat insulating meansbecomes first gradually smaller in cross-section and then graduallylarger in cross-section, said passage having its minimum cross-sectionbetween the ends of said heat insulating means, all of thecross-sections of said passage being circular.

2. In a heating apparatus for heating travelling yarns, in combination,an elongated heating member having a longitudinal, convexly curvedheating surface adapted to be contacted by yarn travellinglongitudinally of said surface; and elongated heat insulating means atleast as long as said heating member formed with a longitudinal grooveopen at one side of said insulating means and in which the entireheating member is located extending longitudinally of said insulatingmeans with said heating surface directed toward said one side of saidinsulating means, the latter having at said groove thereof aconfiguration which forms with said heating surface an elongated passagewhich from one to the other of the ends of said heat insulating meansbecomes first gradually smaller in crosssection and then graduallylarger in cross-section, said passage having its minimum cross-sectionbetween the ends of said heat insulating means, and an elongated closuremember closing said groove at said one side of said insulating means andhaving a longitudinal convexly curved surface directed toward saidheating surface.

3. In a heating apparatus for heating travelling yarns, in combination,an elongated heating member having a longitudinal, convexly curvedheating surface adapted to be contacted by yarn travellinglongitudinally of said surface; and elongated heat insulating means atleast as long as said heating member formed with a longitudinal grooveopen at one side of said insulating means and in which the entireheating member is located extending longitudinally of said insulatingmeans with said heating surface directed toward said one side of saidinsulating means, the latter having at said groove thereof aconfiguration which forms with said heating surface an elongated passagewhich from one to the other of the ends of said heat insulating meansbecomes first gradually smaller in cross-section and then graduallylarger in cross-section, said passage having its minimum cross-sectionbetween the ends of said heat insulating means, and an elongated closuremember closing said groove at said one side of said insulating means and7 8 having a longitudinal convexly curved surface of substan- 2,673,546Newton Mar. 30, 1954 tially the same curvature as said heating surfacedirected 2,7 61,272 Vandamme et a1 Sept. 4, 1956 toward the latter.2,780,047 Vandamme et a1 Feb. 5, 1 957 1 2,864,229 Seem et a1 Dec; 1 6,1958 References Cited in the file of this patent 5 2,864,931 Stoddard etal'. Dec. 16, 1958 3015,5572 Jones Jan. 9, 1962 UNITED STATES PATENTS2,204,603 Kline et a1 June 18, 1940 FOREIGN PATENTS 2,211,141 LobassoAug. 13, 1940 77 ,816 Great Britain May 1, 1957

1. IN A HEATING APPARATUS FOR HEATING TRAVELLING YARNS, IN COMBINATION,AN ELONGATED HEATING MEMBER HAVING A LONGITUDINAL, CONVEXLY CURVEDHEATING SURFACE ADAPTED TO BE CONTACTED BY YARN TRAVELLINGLONGITUDINALLY OF SAID SURFACE; AND ELONGATED HEAT INSULATING MEANS ATLEAST AS LONG AS SAID HEATING MEMBER FORMED WITH A LONGITUDINAL CUTOUTIN WHICH THE ENTIRE HEATING MEMBER IS LOCATED EXTENDING LONGITUDINALLYOF SAID INSULATING MEANS, THE LATTER HAVING AT SAID CUTOUT THEREOF ACONFIGURATION WHICH FORMS WITH SAID HEATING SURFACE AN ELONGATED PASSAGEWHICH FROM ONE TO THE OTHER OF THE ENDS OF SAID HEAT INSULATING MEANSBECOMES FIRST GRADUALLY SMALLER IN CROSS-SECTION AND THEN GRADUALLYLARGER IN CROSS-SECTION, SAID PASSAGE HAVING ITS MINIMUM CROSS-SECTIONBETWEEN THE ENDS OF SAID HEAT INSULATING MEANS, ALL OF THECROSS-SECTIONS OF SAID PASSAGE BEING CIRCULAR.